Process for preparing a laminated heat
shrinkable endless band



NOV. 8, w HARRISON ETAL Re. PROCESS FOR PREPARING A LAMINATED HEATSHRINKABLE ENDLESS BAND Original Filed Dec. 27. 1960 2 Sheets-Sheet 1 JCORONA D1SCHARGE GENERATOR Nov. 8, 1966 .J. w. HARRISON ETAL 25,110

PROCESS FOR PREPARING A LAMINATED HEAT SHRINKABLE ENDLESS BAND OriginalFiled Dec. 27, 1960 2 Sheets-Sheet 2 United States Patent Clfice Re.26,110 Reicsued Nov. 8, 1966 26,110 PROCESS FOR PREPARlNG A LAMINATEDHEAT SHRINKABLE ENDLESS BAND John W. Harrison and Robert D. Lowry,Winchester, Mass., by W. R. Grace and Co., assignee, Duncan, S.C., acorporation of Connecticut Original No. 3,159,520, dated Dec. 1, 1964,Ser. No.

78,649, Dec. 27, 1960. Application for reissue Mar. 16, 1966, Ser. No.538,892

3 Claims. (Cl. 156-184) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

This invention relates to the formation of thick plastic films havingshrinking properties.

Because it is difiicult to extrude and biaxialiy orient thick plasticfilms, e.g., films of thickness over 2 mils, it is an object of thepresent invention to prepare thick biaxially oriented plastic films by anovel procedure.

Another object is to prepare a thick film of irradiated biaxiallyoriented polyethylene having superior shrink energy, greater strength,and improved puncture and abrasion resistance.

A further object is to provide a thick, shrinkable, irradiatedpolyethylene band that is suitable as a binding or fastening agent.

Other objects are to provide a method and apparatus for forming thick,shrinkable, plastic films.

Other objects and advantages of the present invention will becomeapparent in the following detailed description of the invention, whereinreference is made to the accompanying drawings in which:

FIGURE 1 is a schematic representation of the method and apparatus ofthe invention used to prepare the thick shrinking band of plastic film.

FIGURES 2 and 3 disclose one of the many uses of the thick shrinkingbands of this invention.

it is not presently iossible to orient thick irradiated polyethylenefilms and as a result it is not possible to obtain relatively thickheat-shrinkable polyethylene films. Heat shrinking properties areproduced in polyethylene by heating polyethylene film to an elevatedtemperature at which the polyethylene will become stretchable,stretching to orient the heated polymer, and then cooling the polymerwhile under tension to a temperature at which the polymer will retainits stretched or oriented form when tension is released. in effect thepolymer molecules are stretched or oriented and frozen in this stretchedor oriented position. The subsequent application of heat to the polymer"thaws" the polymer and permits the poly mcr molecules to return totheir original non-stretched position.

It has now been found that it is possible to prepare a thick, i.e. over2 mils, irradiated, biaxially oriented polyethylene film which pos essesthe same superior shrinking qualities, high tensile strength and highshrink energy of film of thinner gauge while possessing the increasedstrength of the thicker film. This increased strength coupled with theexcellent shrinking properties make the thickened plastic film suitablefor use in many instances where the thinner film would have beenunsuitable.

This invention results in the production of a thick band, i.c. anendless belt or loop of varying size and width of heat-shrinkable,irradiated polyethylene. The thick bzind is formed by laminating thinsheets of heat-shrinkable polyethylene together. This lamination isproduced without the aid of heat. pressure or adhesive coatings. Theband of film may be as thick as is desired for the particularapplication. Generally 2 to 25 layers will suffice.

Referring to the drawings there is provided a supply roll 2 of 0.8 milthick irradiated, biaxially oriented polyethylene film (Alathon 14irradiated to an extent of about 12 megarads and biaxially stretched350% in each direction) The film 11 is drawn from the supply roll over afirst driven roll 3 and thence over a second drive roll 4. Between thefirst and second driven rolls one surface of the film is exposed to ahigh voltage electric stress created by a corona type, electrostatidischarge apparatus, specifically 21 Howard electrostatic treater whichis a 15,000 volt, single ended neon tube. Located above theelectrostatic discharge apparatus on the opposite side of the film is ametallic surface 12 appropriately grounded. The treated film passesthrough the nip formed by a 3rd driven roll 5 and a first idler roll 6.The idler roll 6 is urged against the 3rd driven roll 5 by a spring. Theidler roll 6 is also movable in a direction away from the driven roll 5.The film, after passing through the nip of the rolls, passes over asecond idler roll 7, over .1 fourth driven roll 8, and thence over the3rd driven roll 5. Between the driven rolls 8 and 5 the surface of thefilm which had not previously been exposed to the electrostaticdischarge apparatus is now electrostatically treated. The film travelsover the third driven roll 5 and into the nip between roll 5 and roll 6where the clectrostatically treated surface of the film passing throughthe nip in the rolls for the second time contacts the clectrostaticallytreated surface of the film passing through the nip for the first time.As the elcctrostatically treated surfaces come in contact they adhere toeach other. The film continues to travel about rolls 5, 7 and 8 until aband of film of sufficient thickness is built up. When a band of desiredthickness has been formed, the idler roll 6 is swung away from drivenroll 5 and the film end may then be cut. The idler roll is swung in aradius pivoted around the center of roll 4 to retain the cut end. Theband is then removed from the rolls.

The idler roll 7 is adjustably mounted on a slotted bar 9. The rolls 8and 5 are mounted in fixed positions. By moving the position of theidler roll 7 along the slotted bar away from or towards the fixed rolls8 and 5 the size of the band of thickened him may be varied within ccrtain limits.

The electrostatic discharge apparatus can be any one of the conventionalcorona diszharge apparatus, including the Howard electrostatic treater,or the Mancib treatcr, or apparatus of the type disclosed in Briti-hPatent 7159M, and British Patent 771,234. Preferably, the coronadischarge apparatus is a neon transformer capable of delivering at least10,000 volts at 5 to 40 milliampcrcs AC. Corona discharge is produced byionizing the gap between a pair of electrodes. The gap between theelectrodes is such that with the application of a particular voltagecorona discharge, without arcing, is obtained.

In general, there is employed in the invention polyethylene film whichhas been irradiated and biaxinlly oriented. The film may be irradiatedto an extent of from 2 to l00 mcgarad, prcfcrably 6 to 20 megnrads. Theirradiation may be accomplished in conventional fashion. cg, by the useof electron beam generators such as the 2 million volt General Electricresonant transformer electron beam gcncrator. The biaxial orientation iscarried out to an extent of Hill to 700% longitudinally and Hill to 900%laterally. The irradiation and orientation may be carried out asdescribed in US. Patent 2,877,500 to Rainer et al. and in the copendingUS. application Serial No. 713,848 filed February 7, 1958, to Baird etaL. both of which are hereby incorporated by reference. The irradiatedand biaxiully oriented polyethylene employed in this invention has atensile strength of at least 5000 psi. at 21 C. and a hrinl; energy ofat least 100 p.s.i. in each direction at 96 C.

The polyethylene film is Du Pont Alathon 14, a high pressure, branchedchain polyethylene having a melt inden of 1.8, an average molecularweight of 20,000 and a density of 0.916. Other polyethylenes withdifferent molecular weights may be employed including low, medium andhigh density polymers produced by high or low pressure techniques andblends of such polymers.

The corona discharge treated irradiated, oriented polyethylene surfacewill permanently bond to a similarly treated polyethylene surfacewithout the use of heat or pressure. This self-adhesiveness is so greatthat the film will tear rather than delaminate.

The irradiated polyethylene film may be uniaxially or biaxiallyoriented. Non-oriented polyethylene and nonirradiated polyethylene donot have this ability to be made self-adhesive by electrostatictreatment.

The strong, shrinkable bands or loops of irradiated polyethylene may beemployed to seal duct work joints, to bind a plurality of objectstogether and may be used to hold lids on containers or barrels. There isshown in FIGURE 2 a metal drum 21, a metal lid 22 which is adapted tocover the open top of said metal drum and which fits over the beaded rimof the drum, and a band 23 of biaxially oriented, irradiatedpolyethylene which is approximately 8 mils thick, 2 inches wide andslightly larger than the outside dimensions of the drum and lid. The lidis fitted upon the drum and the film band is placed around the lid,extending above the drum and below the beaded edge of the drum. The filmband is heat shrunk around the rim and locks the lid to the drum asshown in FIGURE 3.

The invention described in retail in the foregoing specification issusceptible to changes and modifications as may occur to persons skilledin the art without departing from the principle and spirit thereof. Theterminology used is for purpose of description and not of limitation,the scope of the invention being defined in the claims.

We claim:

1. A process for preparing a laminated heat shrinkable endless bandcomprising [orienting] irradiating polyethylene film irradiating saidoriented film] to an extent of 2 to 100 megarads. orienting saidirradiated film. subjecting both film surfaces to corona dischargesufiicient to effect adherence of the surfaces to each other in theabsence of significant heat and pressure, and forming a continuous handfrom said treated film by wrapping a plurality of layers of film about aform.

2. A process for preparing a heat shrinkable laminated endless bandcomprising [biaxially orienting] irradiating polyethylene film [100 to700% longitudinally and 100 to 900% transversely, irradiating saidoriented film] to an extent of 2 to 100 megarads, biaxially orientingsaid irradiated film to 700% longitudinally and 100 to 900%transversely, subjecting both film surfaces to corona dischargesutficient to effect adherence of the surfaces to each other in theabsence of significant heat and pressure, forming a continuous band fromsaid treated film by wrapping 2 to 25 layers of said film about a formand removing the resultant band from said form.

3. A process for preparing a heat shrinkable laminated endless bandcomprising '[biaxially orienting] irradiating polyethylene film [100 to700% longitudinally and 100 to 900% transversely, irradiating saidoriented film] to an extent of 6 to 20 megarads, biaxially orientingsaid irradiated film 100 to 700% longitudinally and 100 to 900%transversely, subjecting one surface of said film to corona discharge,forming a continuous band by wrapping said film about a form, saidtreated surfaces being interiorly positioned, subjecting the exteriorpreviously untreated surface to corona discharge while said film is onsaid form but before it contacts the first treated surface, the coronadischarge treatment being sufiicient to effect adherence of the filmsurfaces to each other in the absence of significant heat and pressure,continuing said wrapping and conora treatment until the resultant bandcontains 2 to 25 laminae, and removing said band from said form.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS 2,388,541 11/1945 Henderson l56-189 2,723,93311/1955 Isenberg 156189 2,810,933 10/1957 Pierce et al l56-272 2,881,4704/1959 Berthold et a1. l$6-272 2,894,139 7/1959 Magruder et al 25049.52,922,883 1/1960 Giaimo 250-495 2,923,964 2/1960 Plonsky 156--2723,018,189 1/1962 Traver 156-272 3,054,708 9/1962 Stainberg 156-2723,067,119 12/1962 Ramaika 156272 3,081,214 3/1963 Strome 156--2723,171,539 3/1965 Holbrook et al. 156-272 EARL M. BERGERT, PrimaryExaminer.

ARTHUR GAUSS, DOUGLAS J. DRUMMOND,

Examiners. R. F. POLISSACK, Assistant Examiner.

